1. Field of the Invention
The present invention relates to a V-type engine for vehicle to be loaded on an all-terrain four-wheel vehicle or a motorcycle and more particularly to a V-type engine comprising a front cylinder unit in a forward slanting position, a rear cylinder unit in a backward slanting position, and a mission chamber formed integrally with a crank case on the back part thereof, the front and rear cylinder units including cylinder heads respectively having a valve driving cam shaft.
2. Description of the Related Art
In this kind of V-type engine with overhead cam shaft for vehicle, a chain mechanism may be used as a cam shaft driving system. Each of cam shaft driving chain mechanisms for a front cylinder unit and a rear cylinder unit is structured so as to respectively wind a cam chain between a sprocket fixed to each cam shaft and a sprocket installed on a crank shaft. The power is directly transmitted to the cam shaft from the crank shaft via the cam shaft driving chain mechanism.
The cam driving chain mechanisms for the front and rear cylinder units are respectively provided with a tensioner. Tension is given to each of the cam chains, thus the cam chains are prevented from looseness, and a good power transmitting condition is kept, and generation of noise is reduced.
Such a cam chain tensioner is arranged on the loosening side of the cam chain and, in accordance with the rotational direction of the crank shaft, for the front cylinder unit, the tensioner is arranged on the rear upper side of the cam chain and for the rear cylinder unit, the tensioner is arranged on the rear under side of the cam chain.
However, in a V-type engine for vehicle in which a mission chamber is formed integrally with a crank case on the back part thereof, the tensioner of the rear cylinder unit is attached so as to be projected backward and downward from the rear cylinder unit toward the mission chamber. Therefore, the space of the mission chamber is restricted forward and upward, and the mission chamber must be formed long in the back-and-forth direction so as to store the mission. Accordingly, the size of the crank case in the back-and-forth direction must be made larger.
Further, the space between the rear cylinder unit and the mission chamber is narrow, so that the removal and adjustment operation for the tensioner for the rear cylinder unit requires a great deal of time. Incidentally, as a document of conventional art, Japanese Patent Publication 63-11174 may be cited.
The present invention was developed in consideration of the aforementioned problems and is intended to devise a power transmitting mechanism from a crank shaft to a cam shaft and arrangement of change gear shafts in a mission chamber, thereby reduce a size of a V-type engine for vehicle in a back-and-forth direction, and facilitate attaching and adjusting operations for the tensioner of a cam chain for a rear cylinder unit.
To solve the aforementioned problems, a V-type engine for vehicle according to the present invention comprises a front cylinder unit disposed in a forward slanting position, said front cylinder unit including a front cylinder, a front cylinder head for said front cylinder, and a front cam shaft arranged on said front cylinder head; a rear cylinder unit disposed in a backward slanting position, said rear cylinder unit including a rear cylinder, a rear cylinder head for said rear cylinder, and a rear cam shaft arranged on said rear cylinder head; a crank case with which a mission chamber is integrally formed at a back part of said crank case; a crank shaft rotatably supported in said crank case; a cam driving intermediate shaft arranged above said crank shaft; a power transmitting mechanism interconnecting said cam driving intermediate shaft and said crank shaft; cam driving chain mechanisms respectively interconnecting said cam driving intermediate shaft and each of said front and rear cam shafts; a change gear input shaft to which a power from said crank shaft is input; a change gear output shaft from which a power is output to an axle of said vehicle, said change gear output shaft being arranged in a back part in said mission chamber; and a tensioner for said cam driving chain mechanism for said rear cam shaft; wherein said change gear input shaft and said tensioner are positioned within a range between a line connecting a shaft axis of said change gear output shaft and a shaft axis of said crank shaft and said rear cylinder unit.
By doing this, a space backward and downward the rear cylinder unit is widely reserved, and the space can be effectively used for an arrangement of the tensioner of the cam driving chain mechanism for the rear cylinder unit, and an arrangement position of the change gear input shaft can be easily changed upward, and the distance between the crank shaft and the change gear output shaft can be shortened, thus a size of the crank case in the back-and-forth direction can be reduced.
Further, in the wide space existing between the line connecting the axis of the crank shaft and the axis of the change gear output shaft and the rear cylinder unit, the tensioner for the cam driving chain mechanism for the rear cylinder unit is arranged, so that the attaching and adjusting operations for the tensioner can be performed easily.
Preferably, the V-type engine for vehicle further comprises a backward idle shaft arranged under said line connecting said shaft axis of said change gear output shaft and said shaft axis of said crank shaft.
By doing this, in correspondence to arrangement of the change gear input shaft upward, the reduction in the size of the crank case in the back-and-forth direction can be realized.
Preferably, the V-type engine for vehicle further comprises a carburetor or a fuel jet device arranged above a V bank formed between said front cylinder unit and said rear cylinder unit.
By doing this, the periphery of the engine can also be made compact and is suited to an engine for vehicle.
Preferably, a center line of a V bank formed between said front cylinder unit and said rear cylinder unit is put into a slightly forward slanting position.
Preferably, said tensioner for said cam driving chain mechanism for said rear cam shaft is disposed on a rear wall of said rear cylinder.